Nuclear Physics Flashcards
What is the de Broglie wavelength of an electron?
λ ≈ (hc)/E
What must the wavelength be to investigate nuclear radius?
Tiny (~10^-15m)
Where does the first minimum appear when investigating nuclear radius?
sinθ =1.22λ/2R
What is the plum pudding model of the atom?
Atoms were spheres of positive charge with tiny negative chargers inside them
Describe Rutherford’s alpha scattering experiment
A circular detector screen set up in front of an alpha source with a strip of gold foil in between
They expected the particles to be deflected by a small amount
Instead most went straight through and some deflected at a large angle
Why in rutherfords experiment did the particles behave the way they did?
Alpha particles went straight through because most of an atom is empty space
Some “hit” the nucleus and deflected backwards or sideways due to positivity charges repelling
In rutherfords experiment when is electric potential energy and kinetic energy the same?
What’s the equation to find it
Alpha particle is deflected through 180 degrees and will reverse in direction
E = (QGold Qalpha) / 4pie Epsilon nought r
As nucleon number increase what happens to radius?
Increases with exponential decay
What’s the equation for nuclear radius being proportional to the cube root of nucleon number
R = R• A^(1/3)
Where R• = 1.4
What are the 4 types of nuclear radiation and what do the consist of?
Alpha - a helium nucleus
Beta minus - election
Beta plus - positron
Gamma - short wave length, high frequency electromagnetic wave
The density of nuclear matter is enormous
True of false
True
What is the ionising strength and speed of the 4 types of nuclear radiation?
Alpha - strong and slow
Beta minus - weak and fast
Beta plus - virtually zero
Gamma - very weak and speed of light
Which type of nuclear radiation is not affected by magnetic field?
Gamma
What are the types of radiation stopped by?
Alpha - paper or few cm of air
Beta minus - 3mm o aluminium
Gamma - many cm of lead or several m of concrete
What is different about beta plus decay compared to the other nuclear radiation?
Annihilated by and election which means it has virtually zero range
What is ionisation?
Addition or removal of an electron from an atom
What the the ionising properties of alpha particles?
Easily pull electrons off atoms
Transfer of energy from the alpha particle to the atom
What the the ionising properties of beta particles?
Knocks electrons off atoms due to very high speeds
Used for controlling thickness of materials
What the the ionising properties of gamma rays?
Radioactive tracers used to help diagnose patients with the need for surgery
Treatment of cancer Tumours
What damage do the types of nuclear radiation have on the body?
Alpha - will not penetrate skin
Very dangerous if
Ingested
Beta - less damage to the body tissue
Gamma - no effect unless long term exposureWhat does a Geiger counter detect?
Radiation
What is background radiation?
Radiation that is all around us
What are 5 sources of background radiation?
The air The ground and buildings Cosmic radiation Living things Man-made radiation
Why is there background radiation in the air?
Radon gas released from rocks(alpha)
Usually Largest contributor
All rock contains radioactive isotopes. True or false
True
What is cosmic radiation?
Cosmic ray particles (Mostly high energy photons) collide with atmosphere
The intensity of gamma radiation obeys what law?
Inverse square law
What does the inverse square law mean?
Radiation spreads out as you get further away
You should keep the radioactive source as far away from your body as possible? Why is this?
Inverse square law
Explain in short 4 points an investigation to show the inverse square law
- Set up a Geiger counter in front of a meter rule
- Place radioactive source (using tongs) at a set distance away and take a reading
- Repeat 3 times for an average
- Repeat for different distances
Make sure you minus the background radiation!!!!!!!!!
every isotope decays at a different rate
i didn’t know how to make this a flash card but it seemed important
radioactive decay is of what distribution?
random
can you predict the decay of a single nucleus?
no
what is the activity of a sample?
the number of nuclei (N) that decay each second
its proportional to the size of the sample
what is activity measured in?
becquerels, Bq
1 Bq = 1 decay per second
what is the decay constant symbol?
lambda
the bigger the decay constant the …
faster the rate of decay
what is the definition of half life?
the average time is takes for the number of unstable nuclei to halve
how does the number of undecayed particles decrease?
exponentially
how do you find the number of atoms if you are given the molar mass?
number of moles multiplied by Avogadro’s constant
what are the 2 main uses of radioactive substances?
radioactive dating (carbon 14 has a half-life of 5730 years and starts to decay once a plant dies. it is take in bt living things during photosynthesis) and medical diagnostic (tracers)
when does alpha emission occur?
in heavy nuclei e.g. uranium an radium
when does beta minus emission occur?
neutron rich nuclei
when does gamma radiation occur?
too much energy
what is emitted in beta minus decay?
electron and an antineutrino
what happens in beta minus decay
neutron changes into a proton
What happens in nuclear fission?
An unstable nuclei splits into two smaller nuclei, and releases some NEUTRONS and ENERGY
what classifies as a large nuclei?
at least 83 protons
large nuclei split into 2 smaller nuclei what is this?
fission
why are the 2 types of fission?
induced and spontaneous
How can we induce fission?
By making a neutron enter a Uranium-235 nucleus, causing it to become very unstable
What kind of neutrons can be captured for induced fission?
Low-energy (“thermal”) neutrons
Why is energy released during nuclear fission?
Because the new, smaller nuclei have a higher binding energy per nucleon
What kind of nuclei are most likely to spontaneously fission?
Large ones
What limits the number of nucleons that a nucleus can contain?
Spontaneous fission
What do nuclear reactors use as fuel for fission reactions?
Rods of uranium (that are rich in U-235)
What isotopes of uranium are found in the uranium rods used for fission reactions?
U-235
U-238
How are uranium rods placed into the nuclear reactor, and why?
Remotely, to keep workers as far away from radiation as possible
Describe the chain reaction in nuclear reactors
A fission reaction produces more neutrons, which then induce other nuclei to fission, which produces more neutrons, etc.
How are produced neutrons slowed down for capture by the uranium nuclei in a chain reaction in a nuclear reactor?
By a moderator (e.g. water)
What are slowed-down neutrons called?
Thermal neutrons
What does the moderator do?
Slows down neutrons so they can captured by uranium nuclei
How does the moderator slow down neutrons?
Elastic collisions between the neutrons and nuclei of the moderator material
What defines the most efficient materials for being a moderator?
Similar mass to the neutrons (e.g. water)
What is the minimum amount of fuel you need to make the chain reaction continue on its own at a steady rate?
Critical mass
What is called when you DON’T have the minimum amount of fuel you need to make the chain reaction continue on its own at a steady rate?
Sub-critical mass
What is the amount of fuel a nuclear reactor uses called?
Supercritical mass
How do you control the rate of fission in a nuclear reactor?
Inserting control rods at varying rates
How do control rods control the chain reaction?
Limiting the number of neutrons in the reactor
They absorb neutrons so that the rate of fission is controlled
What are control rods made of?
A material that absorbs neutrons (e.g. boron)
How do you shut down a nuclear reactor in an emergency?
Releasing all of the control rods into the reactor
How is produced heat removed form the nuclear reactor?
Using a coolant
often the same water used as the moderator
How can a nuclear reactor be used to generate electricity?
Heat from the reactor is used by the coolant to make steam for powering electricity-generating turbines
How do you prevent radiation from escaping the nuclear reactor?
Shielding, often a concrete case
How do you reduce the risks involved with using nuclear power?
Shielding and control rods
How can explosions happen in a nuclear reactor?
Runaway chain reaction
Why is nuclear fission better than fossil fuels?
Creates less greenhouse gases
Why is nuclear fission worse than fossil fuels?
Lots of dangerous waster products
What do the waster products of nuclear fission contain?
High-neutron isotopes, making them unstable and radioactive
How can the waste products of nuclear fission be useful?
Tracers in medical diagnosis
What is the temperature of material removed from a reactor?
Very hot
How is material removed from the reactor cooled?
Remotely placed into a cooling pond
How is radioactive waste stored?
In sealed containers until activity has reduced
What is nuclear fusion?
Two light nuclei combine to create a larger nucleus
Why is energy released during nuclear fusion?
The new nuclei has a much higher binding energy per nucleon
What is the charge on all nuclei?
Positive
Why do nuclei need lots of energy to fuse?
There is an electrostatic force of repulsion between all nuclei that must be overcome
to get close enough to fuse
What fundamental interaction occurs during nuclear fusion?
Strong interaction holds the nuclei together
How much kinetic energy is needed to make two nuclei fuse together?
About 1 MeV
What happens to low-energy nuclei, that try to get close enough for nuclear fusion?
Deflected by electrostatic repulsion
What happens to high-energy nuclei, that try to get close enough for nuclear fusion?
Overcome electrostatic repulsion and are attracted by the strong interaction
What is the mass defect?
Mass of nucleus is less than the mass of its constituent parts
(The difference is the mass defect)
What happens to the the lost mass of a nucleus when nucleons join together?
Converted into energy and relased
What is the energy released when nucleons join together equivalent to?
Mass defect
How much energy is required to pull a nucleus completely apart?
The same as the energy released when the nucleus is formed
What is the binding energy divided by the mass defect equal to?
About 931.5 MeVu⁻¹
At what value of N is Average Binding Energy Per Nucleon at a maximum?
N = 56
Iron
What is the average binding energy per nucleon equal to?
Binding energy divided by nucleon number
What element is the most stable nuclei?
Iron
What happens to the left of Iron on the Binding Energy-Nucleon Number graph?
Fusion
What happens to the right of Iron on the Binding Energy-Nucleon Number graph?
Fission
What does the change in Average Binding Energy give?
Energy Released
What is energy released equal to?
Average binding energy
Why is ionising radiation dangerous?
It ionises body tissue, causing damage
Why are alpha-sources suitable for smoke alarms?
They allow current to flow, but won’t travel very far.
What kind of source is best for smoke alarms?
Alpha-sources
Why might a nucleus be unstable?
Too many neutrons
Too few neutrons
Too many nucleons
Too much energy
